After a stroke occurs, the brain up-regulates several repair pathways in an attempt to heal itself. One of the reasons for limited efficacy of this repair process lies in the presence of growth inhibitory factors in the injured region of the brain. Here, we propose to investigate the influence of signaling via the axon guidance molecule semaphorin 3A (Sema3A) on the recovery process after experimental stroke. Our hypothesis states that, analogous to its function in the developing brain, Sema3A acts as a repellent for growing axons and endothelial cells during adult neurogenesis and revascularization, and that this activity will be detrimental for the recovery process. Our pilot data suggest that i) Sema3A and its receptor neuropilin-1 (NRP-1), are up- regulated in the ischemic brain; ii) recombinant Sema3A leads to axon retraction in cultured cortical neurons, and inhibits tube formation in a brain endothelial cell line; and iii) Sema3A signaling can be disrupted by inhibition of 12/15-LOX. To expand these findings, we propose the following specific aims. In Aim 1, we use cultured primary neurons and a brain microvascular endothelial cell line to study the signaling pathways through which Sema3A operates. Both axonal pathfinding in neurons and development of new blood vessels following experimental stroke may be crucial for stroke recovery, and both are impacted by Sema3A. We will focus on signaling through the MAP kinase proteins, and on metabolites of 12/15-lipoxygenase, which have been shown to mediate the repulsive actions of Sema3A. In Aim 2, we study the expression of Sema3A and its receptor Neuropilin 1 (NRP1), in a mouse model of middle cerebral artery occlusion (MCAO). We will investigate differential effects of sema expression on neurogenesis-related axonal connectivity and the formation of brain microvessels, and correlate levels of Sema3A with functional recovery. In Aim 3, we inhibit axonal pathfinding of newly born neurons by injecting soluble semaphorin on the ipsilateral side of the brain subjected to MCAO. Alternatively, we disrupt semaphorin signaling by injecting an inhibitory peptoid, and by inhibiting the downstream mediator 12-lipoxygenase. Endogenous repair processes activated after stroke can potentially restore functionality to the damaged brain. Can manipulating the semaphorin pathway lead to more efficient integration of neurons and an improved revascularization? This application is relevant to PA-08-099 Mechanisms of functional recovery after stroke.